'Tell people not to panic': Experts say Canada's caterpillar and worm infestation will end

The crawling critters of spring may look gross, but they're nothing to worry about

People across the country are feeling overrun by caterpillars. (Cooper Kennedy)

Nicole MortillaroSenior Writer, Science and Technology

Nicole has an avid interest in all things science. As an amateur astronomer, Nicole can be found looking up at the night sky appreciating the marvels of our universe. She is the editor of the Journal of the Royal Astronomical Society of Canada and the author of several books.

Maybe you're in Toronto, sitting on a patio, finally enjoying some warm weather, only to have them rain down on your table. Or maybe you find the ground covered with them in Saskatoon as you walk out to your garage.

Caterpillars. They seem to be everywhere.

From the Prairies to the east coast, Canadians are battling creepy crawlers that seem to be out in abundance this spring.

In Ontario, there's an infestation of cankerworms (also known as inchworms). Saskatchewan is battling tent caterpillars. Manitoba has both of these as well as elm spanworms, prompting some to call it the "year of the caterpillar," while there's a "plague" of crane fly larvae in Newfoundland.

Just how bad do some people have it? Here's what it looked like for Tammi Hanowski at her home south of Saskatoon.

"No matter what you do — you'll sweep them, you'll vacuum them — and in 10 seconds it's like they're just there again," she told CBC 's Creeden Martell.

While it may seem like a sign of biblical end times to some, it's all part of a natural cycle — though not one entomologists completely understand.

"This is typical of these cycles that are anywhere between eight and 12 years," Judith Myers, of the University of British Columbia's zoology department, told CBC News.

"It's very, very difficult to find what the actual factor is that causes some outbreaks to be longer than others, some declines to go lower than others."

Tent caterpillars seem to be taking over trees across several provinces. This one is a forest tent caterpillar. (Erik White/CBC)

That's because there are various factors that can influence caterpillars' boom-or-bust life cycle. Things like weather conditions (they prefer dry and warm), the presence of parasitoids (which lay eggs inside the egg sacs of caterpillars in the larval stage), diseases and fungi all influence their numbers.

'Year of the caterpillar'

In the case of tent caterpillars, for example, the moths produce eggs sacs where the larvae develop before going into a dormant phase called diapause. In spring, the larvae hatch and emerge as the worms we're now seeing feast on our trees.

And if the conditions are right — such as a warm, dry spring that many parts of the country experienced last year — they thrive.

'They will go away'

All these caterpillars may be an eyesore, but they're nothing to worry about, Myers said.

"Tell people not to panic about the caterpillars," Myers said. "They will go away."

Greg Pohl, an insect and disease identification officer with Natural Resources Canada, said the influx of cankerworms is also not a big deal.

Leaves eaten by cankerworms. (Havard Gould/CBC)

"There are always outbreaks someplace in Canada," Pohl told CBC News. "And it's not always in cities, though certainly there've been a lot of outbreaks in urban areas this year."

He said "huge population outbreaks" happen occasionally. "It's just a matter of all the planets lining up in terms of the right weather conditions in the winter and early spring, and the population levels of the things that eat these things, like birds and other insects."

There are more than 500 different species of cankerworms, Pohl said, and they fall under two distinct types — fall or spring, depending on when they lay their eggs. The ones out now are fall cankerworms. You might notice them as bright green worms that sometimes dangle from leaves, or they might be brown.

Cankerworms, also known as inchworms, are invading some parts of the country. (Shutterstock/Conny Skogberg)

The worms and caterpillars consume the leaves of trees, but the leaves will grow back. So while your tree may look pretty sad in June, by August it should be back to its full, green self, Myers said. Unless, that is, it's been stressed for some time or it's faced a few years of outbreaks.

"One year isn't generally enough to cause all the trees to die," Pohl said. "It'll look terrible in the city, and people don't like to see that, but trees are pretty tough."

And while some cities may be thinking about spraying, it might be too late. Pohl said that spraying has be done early in the life cycle — during the larval stage or when worms are young — to be effective. In the meantime, he says there's not much you can do. There is special sticky tape that can be affixed to trees that will trap them. But aside from that?

"The best thing [people] can do is be patient and just accept that the trees are going to look a little ragged this year," Pohl said.